The term "kine" as used herein means color television picture tube.
In order to prevent objectionable variations in the level of the chrominance signals displayed on the screen of a color television receiver, it is well known to employ an automatic chrominance control (ACC) circuit. ACC circuits typically operate in a closed loop configuration and vary the gain of a first chrominance amplifier in response to the amplitude of the color burst component of the received television signal.
The ACC circuitry will not function properly if the ratio of the burst amplitude to chrominance in the received television signal is incorrect. This incorrect ratio may be due to problems originating at the broadcaster's transmitter, or because of reflections of the signal along the signal path between the transmitter and television receiver. Such an incorrect ratio may cause an overload condition to occur. The response of the ACC circuitry is typically not fast enough to prevent an overload condition from being displayed on the screen. The overload may manifest itself as one or more television lines having an objectionably saturated color level which may resemble a smearing effect. In order to solve this problem, chroma overload circuitry is employed to detect an overload condition and control the gain of a second chrominance amplifier accordingly.
An example of chroma circuitry employing a chroma overload detector is known from U.S. Pat. No. 4,054,905(Harwood, et al.). While this circuitry performs well, it has certain features which may make it not optimally suited for integration in modern integrated circuits which tend to be more densely packed than those of a decade ago.
For example, the circuitry of Harwood, et al. requires a zener diode and a relatively large value resistor (approximately 40K ohms). Zener diodes are not readily available in the technology used in the design and manufacturing of today's densely packed integrated circuits, and because large value resistors require too much area, their use is to be avoided, if possible.